Poly­(oxindolylidene arylene)­s (POXINARs), a family polymers with high performance in terms of thermal stability properties and with ether-bond-free aromatic backbones alternating with bulky, torsion resistant oxindolylidene fragments, have been synthesized by superacid catalyzed polyhydroxyalkylation, and their useful physical properties have been assessed to determine their performance as gas separation membranes. The room temperature synthesis allows a variety of fully soluble, high-molecular-weight polymers in a single pot “click” reaction. These polymers can form flexible and transparent films, and they possess high glass transition temperatures (>500 °C); high decomposition temperatures (ranging from 500 to 524 °C); and FFVs (0.130–0.194) comparable to those reported for the polysulfone, polycarbonate, and polyarylate families. However, their selectivity–permeability combinations are very attractive because some fall close to the 2008 upper-bound limits. Membranes made from isatin and 9,9-dimethyl-9H-fluorene (2aD) display P(O2) = 15.4 Barrer for the O2/N2 gas pair and an O2/N2 selectivity of 6.4, whereas for the H2/CH4 gas pair, they display P(H2) = 170 Barrer and a H2/CH4 selectivity of 77.

Physical aging in amorphous polymers causes a decrease in specific volume and thus in the gas transport properties of their membranes. In this work, the effect of simultaneous thermal decomposition of a thermolabile tert-butyl carbonate group, BOC, and cross-linking by a propargyl group (−CH2–CCH) on the gas selectivity–permeability properties of the resulting membranes is studied to learn how membranes with mitigated variations in the gas permeability coefficients with aging time may be produced. The model copolymer is a poly­(oxyindole biphenylylene) that bears BOC and propargyl groups, [(PN-BOC) x -(PN-Pr) y ] n . Systematic studies on the structure/processing/property relationship assessed by TGA, DSC, and permeation measurement using pure gases reveal that a single thermal treatment for 1 h at 240 °C on a neat copolymer membrane, 12–20 μm thickness, is enough to produce chemically robust membranes (insoluble in NMP and DMSO) and that are physically more resistant to aging since the permeability reduction rate approaches zero. The cross-linked membranes possess lower gas permeability coefficients with higher ideal selectivity with respect to the corresponding neat copolymer membranes, i.e., the P(H2) decreases from 60 to 42 Barrers but H2/CH4 selectivity increases by a factor of 2 (21 to 40), and in general the selectivity–permeability properties for the gas pairs H2/CH4, O2/N2, and CO2/CH4 do not present drastic variations with aging time at least from 72 to 2000 h.

Novel mixed matrix membranes (MMMs) based on fluoropolymers with m- and p-terphenyl fragments and NaX zeolites were prepared. The fluoropolymers were synthesized by a one-pot, room-temperature, metal-free superacid-catalyzed stoichiometric and nonstoichiometric step polymerization of 2,2,2-trifluoroacetophenone with two multiring aromatic nonactivated hydrocarbons (p-terphenyl and m-terphenyl). MMMs were characterized by scanning electron microscopy (SEM) and infrared (Fourier transform infrared (FTIR)) spectroscopy and used in gas permeability tests. SEM analysis showed interfacial voids in MMMs prepared in N-methyl-2-pyrrolidone (NMP), The interfacial adhesion in the polymer–zeolite system was considerably improved when chloroform was used as a solvent. Permeability coefficients for pristine polymer membranes were 1.3-fold higher in CHCl3 than in NMP for p-terphenyl fragment and 2.0 times higher in NMP than in CHCl3 for the polymer with m-terphenyl fragment. The incorporation of NaX zeolites in the polymeric matrices improved the gas permeability coefficients compared to the pristine membranes. The effects of polymer architecture, casting solvent, and interaction between the organic matrix and the inorganic particles on the gas separation performance of the developed MMMs were investigated.

This work studies useful routes to produce cross-linked poly(oxyindole biphenylylene) bearing a crosslinkable propargyl group, PNPr. Thus, the effect of crosslinking temperature and time on gas permeability and ideal selectivity for a non-cross-linked PNPr membrane to produce a cross-linked PNPr membrane is studied in detail in order to learn how more productive membranes, in terms of permeability−selectivity combinations, and membranes resistant to solvent swelling and CO 2 plasticization may be produced. Systematic studies on structure/processing/property relationship assessed by Fourier transform infrared attenuated total reflectance (FTIR-ATR), gel content (GC [%]), swelling degree (SD [%]), specific volume, wide-angle X-ray diffraction (WAXD), and gas permeability measurements reveal that PNPr membranes cross-linked under vacuum (1 mmHg) at 190 °C for 24 h, and further vacuum-annealed for 1584 h, at 35 °C and 10 −3 mmHg, produce membranes that overcome the typical trade-off between permeability and selectivity. In effect, the thermally cross-linked membranes annealed under vacuum for 1584 h, as compared to the non-cross-linked membranes, possess P(H 2 ) and P(CO 2 ) that increase by 2.4 and 2.1 factors while selectivity increases from 25 to 45 for the H 2 / CH 4 pair and from 25 to 39 for the CO 2 /CH 4 pair, whereas P(O 2 ) increases by a 2.4 factor with an associated increase in selectivity from 4.4 to 9.6 for O 2 /N 2 which situates this membrane above Robeson's 2008 upper-bound limit, at least for this pair of gases. The cross-linked membranes are resistant to solvent selling, since their SD [%] in NMP is on the order of 1−3%, and also to CO 2 plasticization since the plasticization pressure was not observed at least up to the 18 bar upstream pressure studied here.